HVAC systems can be used to regulate the environment within an enclosure. Typically, an air blower is used to pull air from the enclosure into the HVAC system through ducts and push the air back into the enclosure through additional ducts after conditioning the air (e.g., heating or cooling the air). For example, a gas furnace, such as a residential gas furnace may be used to heat the air.
In a residential gas furnace, a combustion air inducer is turned-on when a heating call from a thermostat is received. The combustion air inducer is used to draw air through the heat exchangers of the gas furnace for combustion. Once combustion air flow has been established, a pressure switch is closed. The pressure switch is a critical safety feature since, if adequate air flow through the heat exchangers is not established, flames from the heat exchangers could roll-out in an unsafe manner. Once the pressure switch closes to indicate adequate air flow through the heat exchangers, the igniter energizes, the gas valve opens and a flame sensor validates the presence of a flame.